For the level of performance you want and to stay within your PSU limitations, you'll want the new gen of 28nm cards as they're far more energy efficient than the last gen.
If you want something now, I think the AMD 7770 is your best bet. I would recommend this onehttp://www.newegg.com/Product/Product.aspx?Item=N82E16814150599
You get to play all the newest games (the demanding ones at medium quality) with smooth preformance. hopefully they're giving away the free games in Canada too, and you get life-time warranty with XFX plus that card has a better cooler so it'll run quieter and cooler than reference
If you want something from Nvidia, 560-ti will be the best option right now. but that's from the last generation, and ideally I'd say you should wait until a mid-range card with the new 28nm core becomes available
Hope this helps!